There have been demonstrations, including those by the present inventors and their colleagues, in which electromagnetic material response—either previously unobserved or otherwise difficult to achieve in conventional materials—has been obtained in artificially structured materials referred to herein as metamaterials. An example of unusual metamaterial response can be found in negative index metarnaterials, which possess simultaneously negative permittivity (∈) and permeability (μ) over a finite frequency band. The fundamental nature of negative refraction has revealed a key role that metamaterials can play in materials physics, as negative index is a material property not available in existing materials.
A generic description of material response can be found in the Drude-Lorentz model, which leads to the following frequency dispersive forms for ∈ and μ:
            ɛ      ⁡              (        ω        )              =          1      -                        ω          pc          2                                      ω            2                    -                      ω                          0              ⁢              e                        2                    +                                    ⅈΓ              e                        ⁢            ω                                          μ      ⁡              (        ω        )              =          1      -                        ω          pm          2                                      ω            2                    -                      ω                          0              ⁢              m                        2                    +                                    ⅈΓ              m                        ⁢            ω                              These forms, or very similar expressions, have been shown to describe not only conventional material response, but also the response of artificially structured metamaterials. At frequencies greater than the resonant frequency (ω0e or ω0m), either ∈ or μ will have negative values.
Metamaterials can be designed that have either electric or magnetic resonances where there are no equivalent existing materials. Electric and magnetic resonances can be situated at any frequency in metamaterial structures. In particular, by combining electric and magnetic structures, it is possible to arrive at a material with a frequency band over which both ∈ and μ are simultaneously negative. The refractive index, n, for such a material, determined by taking the square root of the product ∈μ, is real, indicating the material is transparent to radiation. However, it has been shown that the correct choice for the sign of the square root is negative when both ∈ and μ are negative. Thus, materials for which ∈ and μ are both negative can be also characterized as negative index materials (NIMs).
Prior art metamaterials include a collection of macroscopic cells that constitutes an array of split ring resonators. These examples are described in previous work by some of the present inventors and their colleagues. U.S. Patent Publication No. US-2001-0038325-A1, and its application Ser. No. 09/811,376, filed Mar. 16, 2001, entitled Left Handed Composite Media are also incorporated by referenced herein.
The demonstration of negative refractive index materials have confirmed various theories concerning the properties that would be possessed by negative refractive index materials. Many basic electromagnetic and optical principles need to be reconsidered as the basic physical explanations have always considered right handed magnetic materials and positive refractive indexes.